In the United States, glaucoma is the second leading cause of legal blindness overall and the leading cause of blindness in African-American individuals (Hiller, R and H. A. Kahn, (1975) Am. J. Ophthalmol 80: 62 and Kahn, H. A. and H. B. Moorhead (1973) US Public Health Service Publication NIH73-427, 120). Primary open glaucoma (POAG) is the most common form of glaucoma affecting 1–2% of the population over age forty (J. M. Tielsch et al., (1990) Arch Ophthalmol. 108: 286). Nearly 12,000 people in the United States are blinded annually by this disorder (H. B. Moorhead (1973) US Public Health Service Publication NIH73-427, 1202–4; J. M. Tielsch et al., (1990) Arch Ophthalmol. 108: 286 and J. M. Tielsch, in Transactions of the New Orleans Academy of Ophthalmology, Ball, S. F. Franklin R. M., Eds (Kugler, Amsterdam, 1993), pp61–68).
Glaucoma is a progressive disease which leads to optic nerve damage and, ultimately, total loss of vision. The causes of this disease have been the subject of extensive studies for many years, but are still not fully understood. The principal symptom of and/or risk factor for the disease is elevated intraocular pressure or ocular hypertension due to excess aqueous humor in the anterior chamber of the eye.
The causes of aqueous humor accumulation in the anterior chamber are not fully understood. It is known that elevated intraocular pressure (“IOP”) can be at least partially controlled by administering drugs which either reduce the production of aqueous humor within the eye, such as beta-blockers and carbonic anhydrase inhibitors, or increase the outflow of aqueous humor from the eye, such as miotics and sympathomimetics.
Most types of drugs conventionally used to treat glaucoma have potentially serious side effects. Miotics such as pilocarpine can cause blurring of vision and other visual side effects, which may lead either to decreased patient compliance or to termination of therapy. Systemically administered carbonic anhydrase inhibitors can also cause serious side effects such as nausea, dyspepsia, fatigue, and metabolic acidosis, which side effects can affect patient compliance and/or necessitate the termination of treatment. Another type of drug, beta-blockers, have increasingly become associated with serious pulmonary side effects attributable to their effects on beta-2 receptors in pulmonary tissue. Sympathomimetics, on the other hand, may cause tachycardia, arrhythmia and hypertension. Recently, certain prostaglandins and prostaglandin derivatives have been described in the art as being useful in reducing intraocular pressure.
While normalization of intraocular pressure can prevent further loss of sight, it cannot alone restore vision that has already been lost. The nerve cells that generate or constitute the optic nerve do, however, retain the natural ability to regenerate the axons (connecting fibers) that populate the optic nerve provided the proper growth factor is present. There is therefore a continuing need for therapies that induce the regeneration of optic nerve fibers that have been lost thereby facilitating restoration of sight.